Diaryl ether

Ullman reaction The synthesis of diaryls by the condensation of aromatic halides with themselves or other aromatic halides, with the concomitant removal of halogens by a metal, e.g. copper powder thus bromobenzene gives diphenyl. The reaction may be extended to the preparation of diaryl ethers and diaryl thio-ethers by coupling a metal phenolate with an aryl halide. 

Oxonium salt formation. Shake up 0 5 ml. of ether with 1 ml. of cone. HCl and note that a clear solution is obtained owing to the formation of a water-soluble oxonium salt. Note that aromatic and aliphatic hydrocarbons do not behave in this way. In general diaryl ethers and alkyl aryl ethers are also insoluble in cone. HCl. 

Concentrated sulphuric acid. The paraffin hydrocarbons, cych-paraffins, the less readily sulphonated aromatic hydrocarbons (benzene, toluene, xylenes, etc.) and their halogen derivatives, and the diaryl ethers are generally insoluble in cold concentrated sulphuric acid. Unsaturated hydrocarbons, certain polyalkylated aromatic hydrocarbons (such as mesitylene) and most oxygen-containing compounds are soluble in the cold acid. 

Carbon-oxygen bonds are formed by the Ullmann reaction (- coupling of aryl halides with copper) which has been varied in alkaloid chemistry to produce diaryl ethers instead of biaryls. This is achieved by the use of CuO in basic media (T. Kametani, 1969 R.W. Dos-kotch, 1971). 

DicblorobenzotnfIuoride. This compound is produced by chlorination of 4-chloroben2otrifluoride and exhibits sufficient activation to undergo nucleophilic displacement with phenols to form diaryl ether herbicides, eg, acifluorofen sodium [62476-59-9]. 

Reaction of bis (sulfonyl chloride)s with diaryl ether produces polyethersulfones. For example, condensation of diphenyl ether with the disulfonylchloride of diphenyl ether yields polyethersulfone (5) ... 

Synthesis. In the syntheses of T and its congeners, formation of the stericaHy hindered diaryl ether core is difficult, as is the introduction of the alanyl side chain (or the preservation of its L (3) absolute configuration) and iodination to the desired degree (T or T. ... 

Aromatic haUdes do not react easily with phenoxide ions to produce diaryl ethers unless the aromatic haUde is substituted with one or more electron-withdrawing groups, eg, nitro or carboxyl groups. The Ullmann reaction uses finely divided copper or copper salts to cataly2e the reaction of phenoxides with aromatic haUdes to give diaryl ethers. 

The reaction gives poor yields of ethers with secondary and tertiary alcohols dehydration to form the corresponding olefin is a more favorable reaction. The reaction fails for the production of diaryl ethers from phenols. 

A variant for the synthesis of diaryl ethers—e.g. diphenyl ether 9, where an aryl halide and a phenoxide are reacted in the presence of copper or a copper-(I) salt, is called the Ullmann ether synthesis. ... 

S Ar reacdons also provide an important strategy for the preparadon of various kinds of diaryl ethers -Dinitrobenzene reacts v/ith even sterically hindered phenols to give the corresponding diaryl ethers fEq 9 3 ... 

Thereacdon of -cyanophenol v/itho-dinitrobenzenein the presence of KFin DMSO gives the corresponding diaryl ether in 95% yield fEq 9 4 ... 

Sjwyer and coworkers have developed an efficient alternative UUmann synthesis of diaryl ethers, diaryl thioethers, and diarylamines using the SnAt reaction. Phenol, thiophenol, or aniline reacts v/ith an appropriate aryl halide, In the presence of KF-aliunina and 18-crovm-6 In acetonitrile or DMSO to give the corresponding diaryl ether or diaryl thio ether as shovm In Eqs. 9.6 and 9.7. ... 

Fragmentation Losses of 1(H), 28 (CO), and 29 (CHO) Daltons are commonly observed for diaryl ethers. In diphenyl ether, m/z 77 is intense, while in phenyl toluoyl ethers m/z 91 is intense, An intense peak in the mass spectra of alkyl phenyl ethers occurs at m/z 94. 

In Figure 13.2, the intensity of the ion at m/z 170 represents a molecular ion of an aromatic compound. The characteristic losses from the molecular ion (M - 1, M - 28, and M - 29) suggest an aromatic aldehyde, phenol, or aryl ether. The molecular formula of Ci2H 0O is suggested by the molecular ion at m/z 170, which can be either a biphenyl ether or a phenylphenol. The simplest test to confirm the structure is to prepare a TMS derivative, even though m/z 11 strongly indicates the diaryl ether. 

The mem-dichlorobenzene complex reacts with protected 0-aryltyrosines to give aryl ethers. Both chlorine atoms can be sequentially substituted to give symmetrical or disymmetrical triaryl diethers (Scheme XVI). The building up of such diaryl ethers from phenolic compounds which have amino groups in their side chains... 

Many reactions have been shown to benefit from irradiation with ultrasound (ref. 19). We therefore decided to investigate the effect of ultrasound, different catalysts and the presence of solids on Ullmann diaryl ether synthesis. Indeed, sonication of mixtures of a phenol and a bromoaromatic compound, in the absence of solvent and presence of copper (I) iodide as catalyst and potassium carbonate as base, produces good yields of diaryl ethers at relatively low temperatures (Fig. 10) (ref 20). 

Fig. 10. Synthesis of diaryl ethers under sonication conditions...

This reaction has been also described for low chlorinated dibenzodioxins. Assuming an identical MS response factor for monoBrDD and monobromohydroxy-biphenyl ether (monoBrDPE) a quantification study shows that monoBrDPE is much more stable towards photolysis compared to monoBrDD, because it accumulates in the mixture of the reaction products. For the dibrominated dibenzodioxins the same reaction (ether fission) is observed but to a minor extent. With triBrDD and higher brominated BrDD no diaryl-ether products are observed at all. 

This reaction is similar to 13-1 and, like that one, generally requires activated substrates. With unactivated substrates, side reactions predominate, though aryl methyl ethers have been prepared from unactivated chlorides by treatment with MeO in HMPA. This reaction gives better yields than 13-1 and is used more often. A good solvent is liquid ammonia. The compound NaOMe reacted with o- and p-fluoronitrobenzenes 10 times faster in NH3 at — 70°C than in MeOH. Phase-transfer catalysis has also been used. The reaction of 4-iodotoluene and 3,4-dimethylphenol, in the presence of a copper catalyst and cesium carbonate, gave the diaryl ether (Ar—O—Ar ). Alcohols were coupled with aryl halides in the presence of palladium catalysts to give the Ar—O—R ether. Nickel catalysts have also been used. ... 

We have studied the thermal decomposition of diaryl ether in detail, since the cleavage of ether linkage must be one of the most responsible reactions for coal liquefaction among the various types of decomposition reaction and we found that the C-0 bond of polynucleus aromatic ethers is cleaved considerably at coal liquefaction temperature. 

Thermal decomposition of seven diaryl ethers at various reaction conditions and the composition of reaction products are shown in Table II. 

TABLE II THERMAL DECOMPOSITION OF DIARYL ETHERS IN TETRALIN... 

Diaryl ether Temp. (°C) Time (min) Conver- sion(%) Products(mol e% of reacted ether)... 

Thus, diaryl ethers with polynucleus aromatic rings were found to be decomposed considerably fast at coal liquefaction conditions. 

Previously we have shown that phenolic compounds have a remarkable positive effect (4) on the coal liquefaction in the presence of Tetralin, depending strongly on the character of coal as well as on the concentration of phenols. The effect of phenols on the decomposition of diaryl ethers will give a good explanation for the previous results, because aliphatic ether structures of some young coals will be decomposed rapidly at relatively low temperatures and so the rate of coal dissolution will not be affected by the addition of phenols, on the other hand, the polycondensed aromatic ether structures will be decomposed effectively by the addition of phenols in the course of coal liquefaction. 

The Effect of Mineral Matters on the Decomposition Ethers. Recently, the effect of mineral matters of coal on the coal liquefaction has received much attention. It was shown that small amounts of FeS or pyrite are responsible for the hydro-genative liquefaction of coal. Therefore, it is interesting to elucidate the effect of mineral matters of coal on the decomposition rate and products of aromatic ethers, and so three diaryl ethers were thermally treated in the presence of coal ash obtained by low temperature combustion of Illinois No.6 coal at about 200°C with ozone containing oxygen. 

TABLE V EFFECT OF COAL ASH ON THE THERMAL DECOMPOSITION OF DIARYL ETHERS (Ethers 4 mmole, Tetralin 40 mmole)... 

Diaryl ether must be one of the important structures responsible for the liquefaction of coal among various oxygen-containing organic structures of coal. 

The rate of decomposition and the distribution of products of some diaryl ethers can be affected in the presence of coal ash. 

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